This invention relates generally to hand trucks or dollies used for moving heavy articles, and particularly to a hand truck which may be converted from use as an upright two wheeled hand truck to a horizontal four-wheeled cart.
The basic two-wheeled upright hand truck has been an indispensable tool in businesses and homes for many decades. Various modifications to the two-wheeled hand truck have been developed to make the hand truck more functional, such as means for securing articles to the frame of the hand truck, supplying the hand truck with powered lifting capabilities, braking and anti-tip mechanisms, or particular combinations of handle placements and positions. Specialized hand trucks have been designed for use in particular applications such as on stairs or ramps, with articles such as drums or bags, or convertible hand trucks with frames having adjustable angles or platforms which allow the hand trucks to be used as portable office utility carts.
One particular development has been the two-wheeled upright hand truck which is convertible to a four-wheeled push cart. One representative example of such a hand truck is shown in U.S. Pat. No. 3,785,669 to Doheny, wherein a pivotable handle mounted near the top of the upright hand truck and having smaller castered wheels attached at the ends thereof may be pivoted relative to the frame in order to bring the handle into an upright position and the wheels into contact with the floor when the hand truck is lowered to a horizontal position.
Another development has been in the area of extensible toe plates for hand trucks, which greatly increase the leverage obtainable in supporting a load compared with conventional hand truck toe plates, but which also allow the user the option of stowing or retracting the toe plate when not in use. One such design is shown in U.S. Pat. No. 4,121,855 to Mortenson.
Similar examples of such hand truck designs can be found in the variety of commercial models which are currently available through such companies as MagLine, Inc. of Pinconning, Mich. and Valley Craft, Inc. of Minneapolis, Minn.
Of particular interest is U.S. Pat. No. 3,193,123 to Wouden, which discloses a convertible four-wheeled hand truck in which the extension to the toe plate comprises a frame member which also serves at the handle when the truck is in the horizontal position, with the handle being couplable to the conventional toe plate by a pair of pronged sleeves.
Although there are several currently marketed hand trucks which have similar frame members serving as the toe plate extensions, and which may be similarly converted to four wheeled use, the concept of attaching to coupling the handle frame to the toe plate was not accepted in the market. This may be due to several drawbacks in the Wouden '123 design, such as the sleeves being separate and distinct, an therefore requiring two hands to properly engage the prongs on the toe plate. If both sleeves are not lifted above the top edge of the toe plate simultaneously, the lower one of the sleeves will prevent the handle frame member from being pivoted close enough to the toe plate to permit the prong on the lifted sleeve to engage the toe plate. The sleeves are also subject to rotating out of alignment on the handle member when not in use, and the prongs of the sleeves present the hazard of snagging or scratching the article being transported. Moreover, the sleeves may not be readily removed or replaced if broken, and cannot be substituted on other hand trucks.